Unvegetated Sand Research Articles

Little change in surface sediment carbon stock following seagrass restoration in Shark Bay, Western Australia

Seagrass restoration might contribute to climate change mitigation efforts by restoring carbon sequestration capacity where it has been lost. However, there have been few empirical investigations into the rate and magnitude of changes in sediment organic carbon stock following seagrass restoration. This study aims to compare patterns of sediment organic carbon stock in the early stages after restoration (6 months, 2 years, 2.5 years, and 5 years) of the seagrass Posidonia australis with adjacent unvegetated sand and continuously vegetated seagrass in Shark Bay, Western Australia. Sediment carbon stock in all restored areas were not significantly different from unvegetated sand, regardless of age. Organic carbon concentrations in surface sediments were similar throughout the top 3 cm. In addition, δ13C of organic carbon of sediment from newly restored seagrass meadows was not significantly different from δ13C of organic carbon from unvegetated sediment. These results indicate that carbon sequestration capacity had not returned up to 5 years after restoration. There is increasing evidence that sediment carbon stocks show little recovery in the early stages of restoration and can take >5 years to return to quantities expected from seagrass meadows.

The Suitable Sites for Seagrass Transplantation in Lae-Lae Island and Sandbar According to Sediment Characteristics

The success of a seagrass transplantation effort depends on identifying locations with optimal sediment characteristics for seagrass growth and survival. This study analyzed sediment characteristics of seagrass bed sediment and adjacent unvegetated sediment on Lae-Lae Island and Lae-Lae sandbar (Makassar, South Sulawesi) to determine the suitable sites for seagrass transplantation. Seagrass bed sediments and adjacent unvegetated sediments were collected from four locations to measure sediment particle size, redox potential, organic matter, water content, nitrate, and phosphate concentrations. Analysis of similarities (ANOSIM) was performed using PAST (Paleontological Statistics) software to determine a suitable site for seagrass planting (transplantation). The results show that surface sediments in the Lae-Lae island are composed of medium sand and coarse sand with grain sizes varying from 0.290 to 0.768 mm, whereas in the Lae-Lae sandbar, the sediment is composed of medium sands (0.371 – 0.460 mm). Redox potential (Eh) varied from -34.1 to -65.7mV, water contents were 1.3 to 1.8%, organic contents were 19.85 to 38.53%, nitrate content varied from 0.60 to 3.47, and phosphate content varied from 7.42 to 14.19 ppm. The percentage of mud (clay and silt) and organic matter were slightly higher in seagrass bed sediments compared to unvegetated area sediments. No differences in nutrient contents (nitrate and phosphate) between seagrass sediments and unvegetated were observed in this study. ANOSIM results show no difference in the sediment characteristics between a seagrass bed and unvegetated sand at the north and south sides of Lae-Lae Island and Lae-Lae sandbar, which means that these three sites are suitable for seagrass transplantation.Keywords: sediment, seagrass, transplantation, site selection, ANOSIM, Lae-Lae

Nearshore seascape connectivity enhances seagrass meadow nursery function.

Diverse habitats composing coastal seascapes occur in close proximity, connected by the flux of materials and fauna across habitat boundaries. Understanding how seascape connectivity alters important ecosystem functions for fish, however, is not well established. For a seagrass-dominant seascape, we predicted that configuration and composition of adjacent habitats would alter habitat access for fauna and trophic subsidies, enhancing nursery function for juvenile fish. In an extensive Zostera marina seagrass meadow, we established sites adjacent to (1) highly complex and productive kelp forests (Nereocystis luetkeana), (2) unvegetated sand habitats, and (3) in the seagrass meadow interior. Using SCUBA, we conducted underwater observations of young-of the-year (YOY) rockfish (Sebastes spp.) recruitment across sites. Using generalized linear mixed effects models, we assessed the role of seascape adjacency relative to seagrass provisions (habitat complexity and prey) on YOY recruitment. YOY rockfish collections were used to trace sources of allochthonous vs. autochthonous primary production in the seagrass food web, via a δ13 C and δ15 N isotopic mixing model, and prey consumption using stomach contents. Overall, seagrass nursery function was strongly influenced by adjacent habitats and associated subsidies. Allochthonous N.luetkeana was the greatest source of energy assimilated by YOY rockfish within seagrass sites. In seagrass sites adjacent to N.luetkeana kelp forests, YOYs consumed higher quality prey, which corresponded with better body condition relative to sites adjacent to sand. Moreover, kelp forest adjacency enhanced YOY rockfish recruitment within the seagrass meadow, suggesting that habitat complexity is a key seascape feature influencing the nursery function of nearshore habitats. In general, to promote seascape connectivity, the conservation and restoration of nursery habitats should prioritize the inclusion of habitat mosaics of high structural complexity and productivity. We illustrate and emphasize the importance of using a seascape-level approach that considers linkages among habitats for the management of important nearshore ecosystem functions.

NO3− circulation and associated driving factors in the unsaturated zone of southwestern Tengger Desert, Northwestern China

In the southwestern Tengger desert in northwestern China, nitrate circulation processes in the unsaturated zone and associated driving factors were studied using water chemistry and stable isotope techniques. At unvegetated sand sites, NO3− content increases from the south to north in the desert. Additionally, a negative correlation (R2 = 0.90, P < 0.005) was evident between the stability of soil NO3− and elevation, suggesting that NO3− storage in soil is significantly influenced by precipitation and temperature. And a significant positive correlation between mNO2−/Cl− in unsaturated zone and elevation (R2 = 0.50, P < 0.0001), indicating both nitrification and denitrification are strongly in the south of desert, however, the nitrification plays a dominant role in the north of desert. Isotopic analyses (δ15N-NO3−, δ18O-NO3−, and δ18O-H2O, δ2H-H2O) of soil pore-water showed that the two dominant NO3− sources were the mixing of atmospheric deposition and soil nitrification, and that the NO3− circulation at the vegetated sand sites was affected by vegetation and animals. Additionally, local environmental conditions lead to complex driving factors, such as the abiotic process of ammonia volatilization of NO3− circulation, which resulted in the 15N enrichment and 18O depletion of residual nitrate in the unsaturated zone of one of the soil profiles. Denitrification was noted in the deep unsaturated zone of two profiles, indicating that the N loss resulted from abiotic versus biotic processes. Analyses of the stable isotope results and the distribution characteristics of NO3− and Cl− suggests leaching of soil NO3− as a result of NO3− in unsaturated zone poses a potential threat to groundwater quality in Dengmaying region. This study suggests that NO3− circulation in the unsaturated zone responds to climate characteristics in the desert ecosystem, and to provide useful information for the protection of groundwater quality in arid desert regions.

Eelgrass meadows, Zostera marina (L.), facilitate the ecosystem service of nitrogen removal during simulated nutrient pulses in Shinnecock Bay, New York, USA

Seagrass meadows are important sites of nitrogen (N) transformations in estuaries, however, the role of N loading in driving relative rates of N fixation and denitrification in seagrass habitats is unclear. The current study quantified N fluxes in eelgrass meadows (Zostera marina (L.)) and nearby unvegetated sand in trials representing in situ and N enriched conditions. Net N2 fluxes were low or negative under in situ conditions in both eelgrass and sand. Under N enriched conditions, denitrification was higher than N-fixation, and denitrification in eelgrass was significantly higher than sand. Denitrification of water column NO3− was more significant than coupled nitrification-denitrification in the eelgrass. Denitrification was likely supported by greater organic carbon and N within the eelgrass sediment compared to sand. Eelgrass meadows in Shinnecock Bay may facilitate the ecosystem service of N removal and retention during short-term nutrient pulses that can originate from groundwater discharge and stormwater runoff.

On the very edge: faunal and functional responses to the interface between benthic seagrass and unvegetated sand assemblages

Changes in macrobenthic spatial structure were investigated across the precise 0.5 m wide boundary zone between intertidal seagrass and unvegetated sand in Moreton Bay, Queensland, Australia. Faunal abundance and species density in the marginal seagrass were only slightly reduced relative to local non-boundary areas. Although gradual diminution in seagrass faunal abundance occurred towards the interface and a few locally dominant species were absent from the boundary zone, most transition was far from gradual, instead being exactly coincident with the specific 0.1 m interface between the 2 habitats. Over this distance, faunal abundance and species density fell by 56 to 60% (from 1412 to 625 m-2 and from an estimated 42 species per sampling horizon to 17, respectively). Dominant seagrass species were abundant right up to the interface itself, but their densities had fallen by 82% a further 0.1 m into the adjacent sand. Functional-group density and diversity mirrored these changes, decreasing over the same distance by 30 to 36%. Spatial analysis showed that adjacent cores along lattice sampling horizons, although spaced further apart, were more similar to each other than were those oriented across horizons, even though these were contiguous. Characteristic high animal species richness in the seagrass relative to adjacent sand appears to be not so much related to characteristics of the seagrass habitat as a whole rather than to the presence or absence of individual plants. Asymmetrically, distributions of species characteristic of the sand stopped somewhat in advance of the interface, leaving a marginal sand zone dominated by generalists occurring at equal (low) species and population density across both habitats.

Edge Effects along a Seagrass Margin Result in an Increased Grazing Risk on Posidonia australis Transplants.

A key issue in habitat restoration are the changes in ecological processes that occur when fragments of habitat are lost, resulting in the persistence of habitat-degraded margins. Margins often create or enhance opportunities for negative plant-herbivore interactions, preventing natural or assisted re-establishment of native vegetation into the degraded area. However, at some distance from the habitat margin these negative interactions may relax. Here, we posit that the intensity of species interactions in a fragmented Posidonia australis seagrass meadow may be spatially dependent on proximity to the seagrass habitat edge, whereby the risk of grazing is high and the probability of survival of seagrass transplants is low. To test this, transplants were planted 2 m within the meadow, on the meadow edge at 0m, and at 2m, 10m, 30m, 50m and 100m distance from the edge of the seagrass meadow into the unvegetated sand sheet. There was an enhanced grazing risk 0-10m from the edge, but decreased sharply with increasing distances (>30m). Yet, the risk of grazing was minimal inside the seagrass meadow, indicating that grazers may use the seagrass meadow for refuge but are not actively grazing within it. The relationship between short-term herbivory risk and long-term survival was not straightforward, suggesting that other environmental filters are also affecting survival of P. australis transplants within the study area. We found that daily probability of herbivory was predictable and operating over a small spatial scale at the edge of a large, intact seagrass meadow. These findings highlight the risk from herbivory can be high, and a potential contributing factor to seagrass establishment in restoration programs.

Stream oxygen flux and metabolism determined with the open water and aquatic eddy covariance techniques

AbstractWe quantified oxygen flux in a coastal stream in Virginia using a novel combination of the conventional open water technique and the aquatic eddy covariance technique. The latter has a smaller footprint (sediment surface area that contributes to the flux; ∼ 10 m2), allowing measurements to be made at multiple sites within the footprint of the open water technique (∼ 1000 m2). Sites included an unvegetated stream pool with cohesive sediment, a macrophyte bed with sandy sediment, and an unvegetated sand bed with rippled bedforms. Nighttime eddy covariance oxygen uptake was always smaller than uptake produced by the open water technique. At the pool and unvegetated sand bed sites, nighttime eddy covariance uptake was 20‐fold smaller than open water uptake. At the macrophyte bed site, gross primary production quantified with the two techniques was similar but eddy covariance uptake was 2.4‐fold smaller. The difference in oxygen uptake between eddy covariance and open water techniques could not be accounted for by uncertainties in the gas transfer velocity but could be accounted for by anoxic groundwater inflow through stream banks outside of the eddy covariance footprint. Nighttime oxygen uptake was also measured with eddy covariance in a tidal freshwater part of the stream, where pore space in the sandy sediment near the sediment–water interface was flushed with stream water at peak water velocities. As a result of this advective hyporheic exchange, nighttime oxygen flux increased fourfold with a doubling of water velocity.

Abrupt transitions between macrobenthic faunal assemblages across seagrass bed margins

The nature of the transition from one contrasting macrobenthic assemblage to another across interfaces between intertidal seagrass and unvegetated sand was investigated in the subtropical Moreton Bay Marine Park, eastern Australia, via six two-dimensional core lattices. The same pattern of transition was manifested in each lattice. Macrofaunal abundance, species density (both observed and estimated total) and assemblage composition did not vary with distance away from the interface within the 0.75 m wide marginal bands of each habitat type. Neither were there significant differences in assemblage metrics or composition between the marginal and non-edge regions of either habitat. There were, however, very marked differences in assemblage composition, abundance and species density across the 25 cm wide strip on either side of the actual interface, the interacting assemblages reacting symmetrically. All these differences therefore took place over an ecotone distance of only 0.5 m at most. Spatial trends in assemblage metrics across the boundary zone were captured accurately by second and third order polynomial regression models. It also appeared that edge effects on individual species within the seagrass were a variable local response not a consistent effect of closeness to the bare sand.

Biodiversity value of a geographically restricted soft coral species within a temperate estuary

ABSTRACT A threatened and uncommon soft coral species, Dendronephthya australis found in large abundance in Port Stephens, within the Port Stephens–Great Lakes Marine Park (PSGLMP), New South Wales, Australia, was hypothesized to be an important habitat for many marine fishes and invertebrates, but is currently under threat from boat anchors, fishing debris entanglement and sand inundation. Surveys were undertaken to assess the biodiversity associated with the soft coral habitat and its adjacent habitats (sponge, seagrass and unvegetated sand), using a combination of Underwater Visual Census (UVC) and Baited Remote Underwater Video System (BRUVS) techniques. In total, 77 fish species and 21 invertebrate species utilized the D. australis habitat, and multivariate fish assemblages associated with soft corals were significantly different to those associated with nearby sponges, seagrass and sand habitats. Species richness of fishes and invertebrates were significantly higher in soft coral and sponge habitats than seagrass. The D. australis habitat was found to be of high importance to juvenile snapper (Pagrus auratus: Sparidae), a species of recreational and commercial fishery importance, which occurred in highest abundance within D. australis, and were significantly smaller in size within the soft coral habitat than the adjacent sponge habitat. Evidently, this rare soft coral habitat supports an extensive marine assemblage, potentially providing a valuable source of food and shelter for fishes and invertebrates, and given it is threatened by human‐induced impacts, its protection should be a priority. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Influence of microhabitat on seedling survival and growth of the mediterranean seagrass posidonia oceanica (l.) Delile

Early life history phases are crucial stages limiting species distribution and abundance, thus influencing assemblage composition in marine benthic environments. In seagrass systems the period between seed germination and establishment is one of the most vulnerable phases for plant development. This study analyzes the influence of microhabitat structure, in terms of substrate nature and algal canopy, on the persistence and growth over two years of seedlings of Posidonia oceanica, the dominant Mediterranean seagrass. Long time persistence of seedlings only occurred on microhabitats providing vegetated rocky substrates, with a maximum value of 81% on rock covered by Cystoseira spp. No seedling was found on unvegetated sand and gravel after the first year. Seedling growth resulted increased on rock covered by Halopteris spp. and Dilophus spp. than on rock covered by Cystoseira spp. Results suggest that high canopy onto a stable substrate enhances seedling persistence, probably because these allow the best anchorage by roots while hampering water flow. In contrast, turf algal cover promotes better seedling growth, possibly through higher light irradiance and nutrient availability. Our findings support the view that the understanding of the factors controlling early life processes is a necessary prerequisite for the comprehension of seagrass species distribution patterns, colonization and recovery potentials, which, in turn, can guide sound strategies for seagrass management and restoration.

The genus Processa in the vicinity of Carrie Bow Cay (Belize) with description of a new species (Crustacea: Decapoda: Processidae)

Three species of the genus Processa are reported from shallow waters of Belize. Processa manningi, sp. nov., a newmember of the burrow-dwelling group, was most commonly found in burrows of the callianassid Neocallichirusgrandimana on a lower intertidal unvegetated sand flat. Both sexes of the new species, sometimes as mated pairs, wereobtained along with the host during sampling of burrows with yabby pumps. Processa bermudensis (Rankin) and Processafimbriata Manning &amp; Chace occurred frequently in sweep net samples taken nocturnally in seagrass beds, but were alsotaken occasionally from interstices of eroded conch shells and other shallow rubble collected in daylight. Coloration is documented, and its utility as a character discussed. The genus has not been previously reported from Belize.

Comparison of hydraulic behaviour of unvegetated and vegetation‐stabilized sand dunes in arid desert ecosystems

ABSTRACTRevegetation was one of most successful measures to restore desert sand dunes and to improve regional eco‐environments in the Tengger Desert, Northwest China. The potential for soil moisture replenishment by precipitation in the revegetation restored desert ecosystems is influenced strongly by the hydraulic properties of the surface soils. Steady‐state infiltration rates from tension disc infiltrometer were measured at revegetation restored desert soils (VS) and unvegetated sand dunes (SD), respectively. Results indicated that the site specific VS and SD hydraulic properties differed significantly. Compared with SD, the long term VS has the effect of decreasing the hydraulic conductivity of the surface soil, while increasing the capillary effect on the infiltration rate. Averagely, the hydraulic conductivity of VS was 0·43 times of SD at the near saturation conditions. At VS, tension infiltration were dominated by capillarity effect more than that of SD, which were ascribed to the differences in soil properties where the former has a higher amount of finer particles, organic matters content and lower bulk densities. Accordingly, the hydraulically functioning mean pore sizes were larger at SD, where the gravity effect dominated the tension infiltration process. Therefore, in the study area under the pulse precipitation events in the growing seasons, VS contains more soil water by capillarity effect than SD does, which would contribute to shallow rooted herbage and cryptogam water consumption. Nevertheless, looking at the whole soil profile, for the actual rainfall water regimes, VS has insignificant effects on the soil profile water regime, with unchanged deep fluxes. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Ecological periodic tables for nekton usage of four US Pacific Northwest estuarine habitats

We compared the species composition and abundance of the total nekton community, using the Bray–Curtis similarity coefficient, and mean total nekton, fish and crab species richness, abundance and biomass, and shrimp abundance across four intertidal habitats in a US Pacific Northwest estuary: (i) eelgrass ( Zostera marina ); (ii) burrowing mud shrimp ( Upogebia pugettensis ); (iii) burrowing ghost shrimp ( Neotrypaea californiensis ); and (iv) unvegetated sand. Field sampling was conducted during daytime high tides, and was quantitative, stratified-by-habitat, randomized, and estuary-wide. More than 10 000 nekton specimens belonging to 64 taxa were collected in 454 samples during 10 sampling periods, each approximately one-month-long (from June to November), over 3 years (1998–2000). Non-metric multidimensional scaling analyses revealed annually recurring across-habitat patterns in total nekton Bray–Curtis similarity. Two-way (habitat, year) analyses of variance revealed annually recurring across-habitat patterns on 10 indicators of nekton-habitat quality and preference. Total nekton species richness, abundance, and biomass were, respectively, on average, 8 ×, 25 ×, and 25× greater in eelgrass, 4 ×, 6 ×, and 5× greater in mud shrimp, and 2 ×, 3 ×, and 2× greater in ghost shrimp, than in sand habitat. Our findings validate the ecological relevance of our habitats to nekton, and suggest they can serve as elements in ecological periodic tables of nekton habitat usage.

Ecological performance and possible origin of a ubiquitous but under-studied gastropod

Invasions by non-indigenous species (NIS) have been suggested to alter local, regional and global biota on unprecedented scales. To manage NIS, it is pivotal to identify whether a species is introduced or native, but even today the geographical origin of thousands of species worldwide remain uncertain. Most of these ‘cryptogenic species’ are inconspicuous and rare, but in a few instances, they can also be abundant and conspicuous species, with large impacts on community structure. The identification of cryptogenic species, and summarizing information on their most likely origin, is an important task in invasion biology, and can highlight the need for research and management. Here, we document that the gastropod Batillaria australis in the Swan River estuary (Perth, Western Australia) is a conspicuous species of uncertain origin. A literature review combined with new survey data revealed that all evidence point to a recent human-mediated transfer; for example, it is absent from the fossil record, was first collected in 1954, has a low parasite diversity, has increased its population size dramatically in recent times, is separated by >3000 km from conspecifics, has no long-distance dispersal mechanisms, and existing ocean currents run against a natural range extension. Surprisingly, despite political and scientific focus on NIS hardly any ecological data have been published on this species from Western Australia. We show that B. australis is highly abundant in both seagrass beds (424 ± 29 ind m −2) and on unvegetated sand flats (92 ± 22 ind m −2) being orders of magnitudes more abundant than any native gastropod in the Swan River. Experiments showed that high resistance to predation and environmental stress potentially explains its success. From our survey data, we calculated that >3.6 billion invasive snails today occupy the Swan River. This large snail populations support other organisms; for example, almost 1 billion macroalgae are found attached to living B. australis and >100 million hermit crabs occupy its empty shells. Given Battilaria’s high abundance, wide distribution, large size, persistent shells that support other organisms and bioturbating behavior, it seems inescapable that this potential invader has impacted the ecosystem functioning of the Swan River. We argue that the search for abundant species of uncertain origin should continue, and that these species generally should be treated with the same interest as high status invaders to mitigate impacts in already invaded systems and to avoid secondary spread into neighboring ecosystems.

Loss of Coastal Strand Habitat in Southern California: The Role of Beach Grooming

We investigated the role of beach grooming in the loss of coastal strand ecosystems. On groomed beaches, unvegetated dry sand zones were four times wider, macrophyte wrack cover was >9 times lower, and native plant abundance and richness were 15 and >3 times lower, respectively, compared to ungroomed beaches. Experimental comparisons of native plant performance were consistent with our survey results: although initial germination was similar, seed bank, survival, and reproduction were significantly lower in groomed compared to ungroomed plots. Rates of aeolian sand transport were significantly higher in groomed plots, while native plants or wrack placed in that zone reduced sand transport. Our results suggest beach grooming has contributed to widespread conversion of coastal strand ecosystems to unvegetated sand. Increased conservation of these threatened coastal ecosystems could help retain sediment, promote the formation of dunes, and maintain biodiversity, wildlife, and human use in the face of rising sea levels.

Edge effects on fish associated with seagrass and sand patches

Seagrass beds form naturally patchy habitats with large areas of seagrass-sand inter- face, or edges. Fish were sampled at 3 sites in the temperate waters of Victoria, Australia, using small (0.5 m wide) push nets at 7 positions: unvegetated sand distant from the patch on the seaward side, the sand edge adjacent to the seagrass on the seaward side, the seagrass edge on the seaward side, the middle of the seagrass patch, the seagrass edge on the shore side of the patch, the sand adjacent to the seagrass on the shoreward side of the patch and unvegetated sand distant from the seagrass on the shoreward side. Samples were taken during the day and night, and seagrass variables were col- lected to describe structural complexity. As expected, more fish were caught in seagrass than over sand. Within seagrass, we found strong and consistent patterns at edges. Regardless of site, the total number of fish sampled was greater at the seaward seagrass edge (484 fish) than in the seagrass middle (231), but there was little difference between the seagrass middle and the shoreward seagrass edge (297). Two species of pipefish, Stigmatopora argus (193) and S. nigra (160), were much more abundant at the seaward seagrass edge than in the seagrass middle at all sites (54 and 46, respec- tively). The goby Nesogobius maccullochi showed a very different pattern. It was more abundant at the shoreward seagrass edge (127) than over the seagrass middle (31) at all sites, and tended to be more abundant over sand at the edge of seagrass patches than in any other sand positions. The weed- fish Cristiceps australis was significantly more abundant at the seaward seagrass edge (26) than in the middle (11), but only at night. Consistent patterns in fish distributions demonstrate clear edge effects both within and alongside seagrass at these sites in south-eastern Australia.

Piping Plovers Nesting Amongst Cottonwood Saplings

Abstract Piping Plovers (Charadrius melodus) typically nest on unvegetated sand or gravel substrates throughout their breeding range. We report on the atypical habitat characteristics of four Piping Plover nests that we found amongst young cottonwood (Populus deltoides) saplings on a sandbar island in the Missouri River along the South Dakota-Nebraska border. Atypical habitat use could have implications for estimating demographic parameters and management of this protected species. It is important to explore the extent to which Piping Plovers use atypical breeding habitat throughout their range and the quality of this potentially poor habitat.

Distribution patterns of benthic juvenile gobies in and around seagrass habitats: effectiveness of seagrass shelter against predators

The significance of a sheltering effect of seagrass against predators influencing the distribution patterns of benthic juveniles of the streaked goby Acentrogobius sp. was investigated by field experimentation in and around seagrass habitats at Moroiso and Aburatsubo Bays, Miura Peninsula, Japan. In the former bay, juveniles were always restricted to the seagrass bed, whereas at the latter, they also occurred over the surrounding bare sand substrate. Juveniles never occurred inside predator-exclusion cages over unvegetated sand in Moroiso Bay. Additionally, a tethering experiment resulted in similarly small numbers of juveniles being preyed upon in both the seagrass bed and over bare sand, suggesting that the predation risk for juveniles may not differ between the habitat types and was thus not responsible for their distribution patterns. The availability of symbiotic shrimp burrows, which were scarce in bare sand in Moroiso Bay but abundant in a similar area in Aburatsubo Bay, was also hypothesized as a determinant of distribution pattern. In a manipulative experiment at Aburatsubo Bay, however, juveniles showed no response to alterations in the availability of symbiotic shrimp burrows, indicating that neither the sheltering effect of seagrass against predators nor the availability of symbiotic shrimp burrows was a significant factor in streaked goby juvenile distribution. Food availability may be a determinant, because food abundance patterns were concordant with the juvenile distribution pattern.

Effects of restoration management on the estuarine isopod Cyathura carinata: mediation by trematodes and habitat change

A restoration programme was introduced in the Mondego Estuary (Portugal) to recover seagrass beds of Zostera noltii endangered by eutrophication. A long-term survey of 10 years was used to assess the development of the processes involved, focusing one of the key species (Cyathura carinata, Isopoda). The mitigation measures implemented since 1998 (nutrient loading reduction, freshwater circulation improvement and seagrass bed protection) enhanced water quality and seagrass recovery, thus preventing the development of macroalgal blooms. C. carinata was resilient to the occurrence of floods and macroalgal blooms, although both events caused dispersion of individuals. This isopod was not much influenced by the changes occurring in the estuary, showing an unalterable population structure during the entire study period. After 1998, its density and biomass became more stable at an inner unvegetated sand flat area, where this isopod was most abundant; its population slightly increased in a bare mud flat at the middle section of the estuary; but it could not establish successfully in a downstream Z. noltii bed, contrarily to other common estuarine species. Apart from other unknown reasons, the disrupted balanced between trematodes and their hosts, caused by the eutrophication processes, may have an important role in the discontinuity of C. carinata at the Z. noltii bed. If the intertidal areas become fully restored to the original seagrass coverage, high prevalence and intensity trematodes may prevent this isopod and other crustaceans from recovering within the intervened areas, by enhancing host mortality and recruitment failure. In order to avoid this kind of situation, it may be necessary to survey the levels of parasite infestation within the target hosts and safeguard areas where crustaceans present healthy populations.